Sailboat Blocks Explained | Expert Advice

In sailing, hardware pulleys are referred to as ‘blocks.’ Blocks are used to create purchase systems, increase mechanical advantage or redirect and guide lines (ropes). There are many different configurations, attachments and design functionalities in the world of sailing blocks today.

Parts of a Basic Block

Bushing- Lining for sheave. Transfers load from the sheave to the cheeks.

Sheave- Wheel with groove for rope to run on.

Cheek- Encloses the sheave. Transfers the load to the straps/strop

Strap or Strop- Lays on top or inside of the cheeks. Straps stop at the top of the block. A strop is a continuous piece which often creates an eye on the top of the block. Transfers load to the eye.

There are a couple terms to know when setting up a purchase. One end attached to a fixed point, and the other is attached to the item that you actually want to adjust with this mechanical advantage. We have the standing part of the line on the fixed point, and then we have the running part attached to maybe a boom or other moving part. The line that you pull on as it comes out of the blocks, this the called the hauling line.

Now, what is the mechanical advantage? All you have to do when you’ve reeved the line through the blocks is count the number of sheaves. Ex: 4:1, 5:1

1. Fiddle Blocks

Fiddle Block

Fiddle blocks offer multiple ‘stacked’ (not side by side) sheaves connected by the cheeks. They work to create in-line purchase systems. Limited to 2 sheaves per block. Fiddle blocks can come in many variations including with and without beckets, swivels, shackles and cam arms. Ideal for 4 or 3:1 in-line systems.

2. Double, Triple Blocks

Triple block

Double or triple blocks offer a way to create larger purchase systems beyond a 4:1. Multiple sheaves are sandwiched together to create these side by side block units. Can be found in many variations.

3. Beckets

Block with Becket

Beckets allow for a dead end to your line. Removable beckets can be easily fitted with an eye splice or you can simply tie your line on using a bowline. Beckets can be found on traditional, fiddle or double and triple blocks. In smaller blocks beckets tend to not be removable, but they often are in larger hardware pieces.

4. Cheek Blocks

Cheek Block

Cheek blocks, or turning blocks, are primarily used to redirect a line. These are often found on the deck and are not associated with a full purchase system.

5. Attachments

Block with Soft Attachment

Blocks offer a few ways to attach to your boat deck or spar. When weight is critical, look for soft Dyneema attachment blocks. These allow you to get rid of the weight of a shackle and maintain a super strong connection. Check these often for signs of chafe.

More traditionally you will find blocks with a shackle attachment. These can either be connected to the strop or on a swivel. For high load applications you will want to look for a forged shackle.

6. Cam Arms

Fiddle Block with Becket & Cam Arm

A cam arm attachment allows you to easily cleat and uncleat your line straight out of the block. This is ideal for mainsheets and some vang systems. These arms typically attache to the cheeks using a series of screws. Parts can differ from one manufacturer to the next, but generally the position and angle is adjustable. You have the ability to completely remove the arm and flip it upside down, or simple adjust the angle up or down to suit your position on the boat.

7. V-Jams & Micro blocks

Micro Fiddle Block with V-Jam

V-jams offer a built in cleat ideal for smaller control lines. A micro fiddle allows for a purchase system to be set up and then cleated- a classic dinghy vang set up.

8. Stand Up Springs & Boots

Stand up Spring

Stand up Boot

Stand-up springs allow a block to maintain their correct orientation when attached to the deck. These keep the block from falling over or getting tangled. Installation can be difficult. The rubber boots offer the same soulution but the rubber sheds the line, where a spring might catch a line easily. Some spring and block assemblies can be found pre-made or attatched to a padeye or car.

9. What is a swivel, free swivel and locked

Block with Swivel

Blocks equipped with a swiveling head often can be locked to a fixed point or left to move freely 360 degrees. Applications like a dinghy mainsheet for instance, you’d want to be able to rotate through when tacking and jibing. In other applications keeping the block fixed will keep a line from tangling. Each manufacturer has a slightly different way to lock and unlock their swivel heads, typically locking in the 90 degree position.

10. Ratchet blocks – Auto & Manual

Ratchet Block

Ratchet blocks are ideal for higher loads that are handled often like mainsheets or spin sheets. Normal Ratchet blocks function in 2 modes, usually set by a ‘switch’ depending on the manufacturer. The ‘free’ mode allows the sheave to spin easily both ways. When the ratchet is turned on, its easy to pull in one direction but will not go backwards helping you to grip and pull in the line. Auto ratchets offer both modes without the manual switch. The ratchet will engage automatically under a certain amount of load and spin freely when load is lightened.